Microwave or millimetre wave items, as follows: (a) Travelling-wave ‘vacuum electronic devices’, pulsed or continuous wave; 1. Devices operating at frequencies exceeding 31,8 GHz; 2. Devices having a cathode heater with a turn-on time to rated RF power of less than 3 seconds; 3. Coupled cavity devices, or derivatives thereof, with a ‘fractional bandwidth’ of more than 7 % or a peak power exceeding 2,5 kW; 4. Devices based on helix, folded waveguide, or serpentine waveguide circuits, or derivatives thereof, having any of the following: a. An ‘instantaneous bandwidth’ of more than one octave, and average power (expressed in kW) times frequency (expressed in GHz) of more than 0,5; b. An ‘instantaneous bandwidth’ of one octave or less, and average power (expressed in kW) times frequency (expressed in GHz) of more than 1; c. Being ‘space-qualified’; or d. Having a gridded electron gun; 5. Devices with a ‘fractional bandwidth’ of greater than or equal to 10 %, with any of the following: a. An annular electron beam; b. A non-axisymmetric electron beam; or c. Multiple electron beams; (b) Crossed-field amplifier ‘vacuum electronic devices’ with a gain of more than 17 dB; (c) Thermionic cathodes designed for ‘vacuum electronic devices’ producing an emission current density at rated operating conditions exceeding 5 A/cm 2 or a pulsed (non-continuous) current density at rated operating conditions exceeding 10 A/cm 2 ; (d) ‘Vacuum electronic devices’ with the capability to operate in a ‘dual mode’; Technical note : ‘Dual mode’ means that the ‘vacuum electronic device’ beam current can be intentionally changed between continuous-wave and pulsed mode operation by use of a grid and produces a peak pulse output power greater than the continuous-wave output power.